1. Technical Field
The present invention generally relates to a frequency reflecting unit, more particularly, to a frequency reflecting unit having a three dimensional structure.
2. Description of Related Art
A frequency reflector is generally used on an elliptical dish antenna reflector, and may be designed to have band-stop frequencies covering a wide frequency range. The frequency reflector is applicable to radars on the ground or missiles in the air to shield the antennas installed on the radars or the missiles from most of the electromagnetic waves to protect the antennas from being interfered with by environmental noise.
Conventionally, the frequency reflector is implemented by a metal radome, which is applicable to airplanes, missiles, and navigation. However, since the metal radome is too large in size, the frequency reflector based on the metal radome is not suitable for use in portable electronic apparatuses. Therefore, a frequency reflector including the metal pattern and a dielectric substrate has been provided. On the positive side or the back side of at least one layer in the dielectric substrate are disposed periodically arranged metal patterns, for example, a cross-shaped or U-shaped metal pattern.
The frequency characteristics of the frequency reflector depend on the interactions between the periodically arranged metal patterns and electromagnetic waves. Thus, the frequency reflector exhibits excellent selectivity with respect to the electromagnetic waves within the band-pass frequencies, while reflecting the electromagnetic waves within the band-stop frequencies. Since band-pass filters can selectively filter out undesired noise, band-pass filters are widely used in electromagnetic interference (EMI) protection.
In the prior art, to lower the band-pass frequencies and the band-stop frequencies for the frequency reflector, a capacitor or an inductor is required to be attached onto the two-dimensional surface of the frequency reflector. In other words, the attachment of a capacitor or an inductor to lower the band-pass frequencies leads to an increased area of the frequency reflector that limits the applications of the frequency reflector. Therefore, there is a need to provide a frequency reflector without increasing the area, while lowering the band-pass frequencies and the band-stop frequencies for the frequency reflector.